It is well known that any significant reduction or restriction in the flow of blood through the arteries of the body can cause complications which may have serious consequences. Arterial blockages caused by plaque and fibrosis build-up in the arteries are known to be a leading cause of heart attacks, strokes, and other debilitating maladies. Accordingly, it is extremely important for the health of a patient that any stenosis, or blockage, which is causing such a condition, be eliminated or reduced.
Fortunately, with the advent of so-called bypass surgery techniques, the consequences of blockages in various arteries can be alleviated by grafting replacement arterial tissue to the affected artery. In this manner, blood is allowed to bypass the blockage in the affected artery and the blood supply to the body tissue which is downstream from the blockage is thereby restored. While bypass surgical procedures have become relatively safe, reliable, and effective, portions of the body must nevertheless be opened to accomplish the surgery. In other words, bypass surgery is invasive, and can consequently require significant post-operative recovery time. To avoid the drawbacks associated with invasive bypass surgery, less invasive surgical procedures have been developed wherein a device is inserted into the bloodstream of a patient and advanced into an artery to reduce or remove an arterial stenosis.
One well known and frequently used procedure to accomplish this task is popularly known as angioplasty. For a basic angioplasty procedure, a dilating balloon is positioned across the particular stenotic segment and the balloon is inflated to open the artery by breaking up and compressing the plaque which is creating the stenosis. The plaque, however, remains in the artery and is not removed. Unfortunately, in some cases, it appears that the plaque which remains in the artery may still present a stenosis. Furthermore, in approximately 30-60% of the vessels treated by angioplasty, there is a re-stenosis. This high recurrence rate is thought to be the result of fibrotic contraction in the lumen of the vessel. In these situations, other more drastic procedures need to be employed.
As an alternative to angioplasty, atherectomy procedures have been developed to resolve the problems caused by blocked arteries. However, unlike an angioplasty procedure which opens the stenosis in the artery but does not remove the plaque which caused the stenosis, an atherectomy procedure mechanically cuts and removes the plaque which is creating the stenosis from the artery. Many examples of such cutting devices can be given. For instance, U.S. Pat. No. 4,895,166 which issued to Farr et al. for an invention entitled "Rotatable Cutter for the Lumen of a Blood Vessel", and which is assigned to the same assignee as the present invention, discloses such a cutter. U.S. Pat. No. 4,589,412 which issued to Kensey for an invention entitled "Method and Apparatus for Surgically Removing Remote Deposits" is but another example.
Fixed atherectomy devices are typically limited to producing cutting paths having diameters less than or approximately equal to the insertion diameter of the devices. Accordingly, expandable cutting atherectomy devices have been developed which allow cutting paths having diameters greater than the insertion diameter of the devices. Examples are disclosed in U.S. Pat. No. 4,966,604 which issued toe Reiss for an invention entitled "Expandable Atherectomy Cutter with Flexibly Bowed Blades", and U.S. Pat. No. 4,986,807 which issued to Farr for an invention entitled "Atherectomy Cutter with Radially Projecting Blade", both of which patents are assigned to the same assignee as the present invention. These devices expand their cutting surfaces after insertion into the vessel to be cleared.
A common characteristic of the foregoing fixed and expandable atherectomy devices is that they all produce cuttings from the stenosis which must be collected and removed from the artery. This collection of cuttings is necessary to prevent the cuttings from forming another blood vessel blockage. Angioplasty procedures, however produce no cuttings and correspondingly do not require cutting collection. Unfortunately, standard angioplasty sometimes results in only a small opening through the stenotic segment of the artery. To overcome this problem, improved angioplasty procedures have been developed which do not produce loose cuttings from the stenosis while they do increase the diameter of the stenotic segment passage beyond the diameter produced by simple angioplasty. One such procedure is disclosed in U.S Pat. No. 4,273,128 which issued to the inventer of the present invention for an invention entitled "Coronary Cutting and Dilating Instrument". According to this procedure, a catheter based device is used to make longitudinal cuts in a stenotic segment of an artery prior to angloplastic enlargement of the segment.
It has been shown that when an angioplasty procedure is performed after the stenotic segment is longitudinally incised, the opening established through the segment is much larger as compared to standard angioplasty without the prior incisions. Still further, the increase in the opening in the stenotic segment is accomplished without the production of cuttings like those resulting from atherectomy procedures and without tearing the vessel wall. Moreover, it has been found that incising the stenosis prior to dilation allows greater compression of the stenotic tissue with decreased likelihood of the stenosis rebuilding at a later date. As those skilled in the art will appreciate, the plaque creating a common arterial stenosis is somewhat fibrous and will tend to return to its original predilation configuration. With this fibrous composition, the stenosis is therefore more likely to maintain a compressed configuration if the fibers are incised prior to balloon dilation. On the other hand, if the fibers in the stenosis is not incised first, the completeness of the compression of the stenosis is dependant on whether the inflated balloon is able to break apart fibers in the tissue. As those skilled in the art will recognize, dilation of a segment is of course limited by the arteries able to withstand dilation. Over-dilation can have the catastrophic result of rupturing the vessel.
While a procedure involving incision before dilation is typically effective, flexibility of the shaft connected to the cutting member can result in diminished surgical control over the cutting member. More specifically, control over the orientation and magnitude of travel of the cutting element is hampered by torsional and longitudinal flexibility of the connecting shaft. For example, a surgeon may want to make a 0.5 cm incision, but, the inherent flexibility of the shaft may result in incisions which are shorter than desired.
In light of the above, it is an object of the present invention to provide an improved device and method for longitudinally incising a stenotic segment of an artery prior to an angioplasty procedure. It is another object of the present invention to provide a cutting device which, in cooperation with an angioplasty procedure, is able to produce an opening in a stenotic segment where the diameter of the opening is greater than the insertion diameter of the device. It is yet another object of the present invention to provide a device insertable into an obstructed artery which incises a stenosis without producing potentially harmful cuttings. It is also an object of the present invention to provide a device which allows improved control over the length of the incisions produced in the stenotic segment. Yet another object of the present invention is to provide a device which is flexible enough to allow advancement of the device through narrow vessels and around sharp turns. Still further, it is an object of the present invention to provide a device for longitudinally incising a stenotic segment of an artery which is relatively easy to manufacture and is comparatively economical.